Maine's stay at home order was updated yesterday. Pursuant to that order "construction and maintenance of essential infrastructure" can continue. Admittedly, that can sound pretty limiting.
Notably, though, businesses identified by CISA's federal guidelines as "essential" will also be considered essential in Maine. And, under those guidelines, construction workers that are performing work necessary for the safety, sanitation, and essential operation of residences, businesses, and public works will be entitled to carry on with their work. So, if the roofing work is necessary for the safety, sanitation, and operation of the building, then it'd follow that roofing work could be deemed essential.
Finally, it's important to remember that these ordinances and regulations can change in a hurry - after all, Maine's changed yesterday. So, it'd be wise to be on the lookout for announcements from local and state governments. Additionally, this tracker from Levelset should be useful: Can I do Construction Work In my State?